I. Field of the Invention
The present invention relates to wastewater systems, and especially to those wastewater treatment systems which are packaged, containerized units.
II. Description of Prior Art
In the treatment of wastewater, there is often utilized a containerized or packaged unit treatment plant which treats received wastewater on an intermittent or small flow basis, such as from a home, small apartment building, or the like. In the home construction industry, for example, a buried, subsoil sewage treatment vessel or septic tank is often used for primary treatment of wastewater. Such sewage treatment devices usually receive flow intermittently and at low hydraulic loading rates and must treat the intermittent flow to meet environmental and health standards. Oftentimes, the unit is merely a holding or "septic" tank that removes settleable solid waste from the wastewater stream.
It is desirable that wastewater be treated in an economical way using as little energy as possible and as few moving parts as possible, while removing a high percentage of solid material from the wastewater stream, and while lowering the chemical oxygen demand (COD) and the biochemical oxygen demand (BOD) of the wastewater stream. It is desired that a minimum of sludge removal would be required since sludge disposal presents an extra problem.
Waste material entering the unit is normally heterogeneous in nature, containing solid waste material as well as liquid wastewater. It is desirable that a wastewater treatment apparatus produce a total homogenation of the fluids received from the waste stream so that they may be properly biodegraded.
In aerated treatment systems, there is often a problem of clogging of the aeration assembly, or diffuser, which provides oxygen and mixing to the unit. Such clogging will cause a degeneration of the treatment process or possibly a total stoppage of air flow to the vessel, converting the process conditions from aerobic to anaerobic, thus removing most of the treatment capability. Also, some aeration assemblies are prone to movement within the vessel, due to the particular design of the assembly and the flexibility of the piping used in construction. Movement of the aeration assembly is unwanted for two primary reasons. First, the upward flow of bubbles should be directly underneath the influent line so that all incoming wastewater will be immediately subject to aeration. Second, the upward flow of bubbles should be kept close to the influent wall of the vessel so that the desired circular flow is maintained. Therefore, it is desirable that an aeration unit or diffuser be provided that minimizes or prevents clogging by solid material entering the unit or microbial mass produced by the unit, and that is prevented from movement away from the side wall adjacent the influent line.
Perhaps the most troublesome problems encountered by prior art systems, however, are those pertaining to the accumulation of scum or floating material near the effluent line. For example, the portion of the vessel serving as the clarifier often contains floating material which can escape the treatment system via the effluent line along with clarified liquid. Ideally, such solids should not remain in the clarifier portion at all, but should re-enter the aeration portion of the vessel for further biodegradation. One solution to the problem of effluent solids, as disclosed in U.S. Pat. No. 4,834,879, has been to draw the effluent from below the surface of the liquid, and then directing the effluent through multiple turns in an effort to leave as much suspended solids within the vessel. While that device did serve to reduce the solids within the effluent more effectively than its predecessors, environmental laws are becoming increasingly more strict, requiring even further reductions in the amount of solids leaving such treatment systems.
Therefore, there is still a strong need for an innovative wastewater treatment system which: (1) increases the time that settleable solids spend within the aeration section of the treatment vessel, (2) decreases the amount of solids leaving the treatment vessel, and (3) remains as inexpensive and reliable as comparative systems.